ANNAPOLIS—While oyster and striped bass populations are on the rise in the Chesapeake Bay, crab populations continue to fall, and the water body may take decades to show signs of a strong recovery, according to a report released Tuesday by a coalition of governments, environmental organizations and researchers.

The 2013-2014 Bay Barometer is an annual overview of the health of the Chesapeake, prepared by the Chesapeake Bay Program, which includes federal and state agencies, local governments, non-profit organizations and academic institutions.

Between 2013 and 2014, the spawning-age female crab population fell from 147 million to 64.5 million, a 53 percent decline, according to the report.

While it could be climate change, habitat conditions or predators, the crab decline does not yet have a clear cause, said Bruce Vogt, manager of Ecosystem Science and Synthesis for NOAAs Chesapeake Bay Office. Vogt said that even with a 10 percent decrease in crabbing across the bay, populations have been markedly declining.

Despite other ongoing challenges like population growth, climate change and delayed effects of improvement measures, the bay overall is in recovery, Chesapeake Bay Program officials said Tuesday. This years grade of D+ is an improvement over last years D- mark.

A large-scale oyster restoration project set in place in 2010 has been highly successful, said Vogt, and oysters are seeing a 92 percent survival rate in Maryland, according to the Bay Barometer.

Established in 2010, the Bays Total Maximum Daily Load, otherwise known as its pollution diet, stretches across six states—New York, Pennsylvania, Maryland, Delaware, West Virginia and Virginia—and the District of Columbia and regulates pollution of local streams and rivers within the watershed.

It ensures the seven jurisdictions reach all designated pollution controls by 2025, with 60 percent achieved by 2017, according to the EPA.

It could be almost 10 years before you actually see the positive impacts that result from the reduction in pollution, said Nick DiPasquale, director of the U.S. Environmental Protection Agencys Chesapeake Bay Program, (but) our conclusion is that we are witnessing a system in recovery.

Nitrogen, phosphorus and sediment pollution in wastewater is decreasing, but efforts to reduce overall nutrient pollution are lagging behind the goals set out by the EPA, said Rich Batiuk, associate director for science for the Chesapeake Bay Program.

Efforts to reduce nutrient and sediment pollution from urban streets, farm fields and onsite septic systems are lagging behind, according to the report.

It takes time to see the effects of wastewater treatment and to educate farmers on better nutrient management practices, Batiuk said.

Although Gov. Larry Hogan halted new phosphorous-control regulations last month, Maryland must still reach its federal nutrient-pollution goals by 2017 and 2025, DiPasquale said Tuesday.

We probably will not see achievement with the water quality standards by 2025—we will have all of the improvement measures in place to treat water pollution, but we probably wont see the results by 2025, said DiPasquale.